Optical transceiver port

ABSTRACT

A port including a lens for coupling one optical element with another optical element. The lens includes a focusing lens surface that has optical power and a flat lens surface that has little or no optical power. The lens is typically aspherical and couples high angle rays emitted from a source and also introduces aberrations such that the image formed on the receiving optical element is not reflected back to the source optical element. A point is imaged as a spot. The port couples light between optical elements by slightly defocusing the source without impeding the efficiency of the port.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/422,331, filed Oct. 30, 2002 and entitled OPTICALTRANSCEIVERS PORT, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. The Field of the Invention

[0003] The present invention relates to optical transceivers. Moreparticularly, the present invention relates to small form factor opticaltransceivers that couple light by defocusing the image in order toreduce or eliminate reflections back to the light source while stillefficiently coupling the light.

[0004] 2. Background and Relevant Art

[0005] Fiber optic networks often include a transmission side and areceiver side. On the transmission side, it is important that the lightbe efficiently coupled into the transmission fiber V in order to achieveadequate transmission power with minimum laser output strength. On thereceiver side, it is important to efficiently image the fiber outputonto detectors with adequate margin for error. This is particularly trueas the size of detectors decreases, often for cost reasons.

[0006] Effective coupling of the light into the fiber on thetransmission side and effective coupling of the fiber output to adetector on the receiver side is often achieved through the use of smallform factor optical transceivers or coupling elements that are oftenreferred to as ports. Ports are also used for other purposes, such ascoupling the output of an optical fiber to another optical fiber. Ports,which are often formed from ball lenses that are pressure fit to ahousing body, are used because they are small and can typically be massproduced.

[0007] Optical transceivers or ports thus play an important role inoptical networks. As the size of the optical ports decreases, attemptshave been made to produce molded ports that incorporate the opticalaspect or lens of the port into the molded design. This has proven to bea difficult task for several reasons. The molding process needs tosupport the integrity of the optical aspects of the port and the opticaldesign of the port is typically limited by the mechanical limitations ofthe molding process.

[0008] In order to address these constraints, ports have been formedthat assign optical power to each surface of the port lens. When theoptical power of the port lens is divided between two surfaces, bothmaking and designing the port become more difficult for several reasons.The surface accuracy of each surface, for instance, must be analyzed.Also, any positional error between the two surfaces of the port lensreduces the performance of the port lens due to aberrations that arecaused by the positional error. In other words, it is more difficult tomold a port whose optical power is divided across two lens surfacesbecause there are more factors that can reduce the overall performanceof the port.

[0009] Some optical transceivers incorporate ball lenses into theirdesign. When the numerical aperture of the source light is low, a balllens is usually able to couple the light effectively. Unfortunately,many light sources often generate most of the power into the higherangle light rays whose numerical aperture is higher than what the balllens can effectively couple. The higher angle light rays are thus highlyaberrated and are not effectively coupled by ball lenses, and balllenses are unable to properly focus the higher angle light rays on anoptical fiber or other light receiver.

[0010] Another problem with optical transceivers or ports is related tolight reflections that interfere with the light source. When light raysfrom a light source are focused, for example, on an optical fiber, theimage formed on the optical fiber is reflected back through the portlens to the light source. The reflection of light back into the lightsource may interfere with the data that is being transmitted over theoptical network and may reduced the efficiency of both the light sourceand the lens. If the light source is an optical fiber, then thereflections may be transmitted back through the optical network.

BRIEF SUMMARY OF THE INVENTION

[0011] These and other problems and limitations are overcome by thepresent invention which relates to a small form factor opticaltransceiver or port. In one example of the present invention, a lens isintegrated into the port such that the port or optical transceiver is asingle molded optical element. The lens of the port has two surfaces: afocusing surface and a flat surface. The optical power of the lens istypically located in the focusing surface of the lens. This eliminateserrors that are introduced when the optical power of a lens is dividedbetween two surfaces and the surfaces are not positioned correctly withrespect to each other.

[0012] The focusing surface of the lens is usually placed within thebody of the port and supports correct magnification of the light source.The other lens surface is essentially flat and the space between theflat surface and the focusing surface is often filled with moldingmaterial. The flat surface is configured to be placed near the imageposition (on an optical fiber, for example) such that any tilt of theflat lens surface is minimized with respect to the image size.

[0013] The present invention may be used, for example, to couplemultimode vertical cavity surface emitting lasers (VCSELs) with opticalfibers. These VCSELs often produce power in the higher angle light raysthat are emitted from the VCSEL and the lens of the port must be able toefficiently couple the high angle rays to the optical fiber in order toeffectively couple the light. However, the image of the source light canbe reflected back to the source and the reflection of the light sourcecan interfere with the transmission of data in the optical network andis undesirable. The present invention introduces aberrations such thatthe image is defocused without sacrificing the ability of the port toeffectively couple the light.

[0014] The present invention thus relates to a lens that has built inaberration without significantly impacting the ability of the lens tofunction as an optical transceiver. The lens, in accordance with thepresent invention, is thus able to couple a source with a receiver wherethe numerical aperture of the source is higher than the numericalaperture of the receiver. It is not necessary, however, that thenumerical aperture of the receiver be lower than the numerical apertureof the light source.

[0015] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to describe the manner in which the above-recited andother advantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

[0017]FIG. 1 is a perspective illustration of a vertical cavity surfaceemitting laser and illustrates the numerical aperture of the high anglelight rays that are emitted from the surface of the vertical cavitysurface emitting laser;

[0018]FIG. 2 is a plot that correlates the angle of a light ray with theintensity of the light ray and illustrates that the most intense lightrays are the high angle light rays;

[0019]FIG. 3 is a cross sectional view of an optical transceiver or portthat incorporates a lens;

[0020]FIG. 4 illustrates a source whose high angle rays are coupled toan optical fiber using a lens that has optical power in a single lenssurface;

[0021]FIG. 5A illustrates points of light from a light source;

[0022]FIG. 5B illustrates the image or spot size of the points on anoptical fiber of light points that are illustrated in FIG. 5A;

[0023]FIG. 6 illustrates a lens; and

[0024]FIG. 7 plots the ability of a lens to couple light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] As used herein, a “light source” or “source” refers to opticalelements or devices that emit light or light signals. Exemplary opticalelements include, but are not limited to, lasers (vertical cavitysurface emitting lasers (VCSELs), edge emitting lasers, and the like),ports, optical fibers, other optical transceivers and the like or anycombination thereof. As used herein, a “light receiver” or “receiver”refers to optical elements that receive light or that are coupled tolight sources. Exemplary receivers include, but are not limited to,ports, optical fibers, detectors, lenses, other optical transceivers andthe like or any combination thereof. A light source is often coupled toa receiver using an optical transceiver or port that, in accordance withthe present invention, incorporates a lens. This includes, but is notlimited to, using a port or lens to couple a laser light source to anoptical fiber, couple the output of one optical fiber to the input ofanother optical fiber, couple the output of an optical fiber to adetector, and the like or any combination thereof.

[0026] Optical transceivers typically use ball lenses to couple lightfrom a source, such as a VCSEL, to a receiver such as an optical fiber.As previously described, however, ball lenses are unable to efficientlycouple light in some instances because most of the power emitted by theVCSEL is located in the high angle rays that are emitted from the VCSELthat the ball lens cannot properly focus on the receiver. The presentinvention relates to an optical transceiver or port that includes orincorporates a lens that is able to couple high angle rays from a sourceto a receiver. The present invention also introduces designedaberrations such that the image is slightly defocused in order to reduceor eliminate reflections back into the source while still coupling thesource to the receiver.

[0027]FIG. 1 is a block diagram that illustrates a VCSEL, which is oneexample of a multi mode light source. It is understood that the presentinvention is not limited to VCSELs as light sources and that other lightsources, such as edge emitting lasers can be used. Although theoperation of a VCSEL and other light sources is known in the art, theoperation of a VCSEL is presented for clarity. In a VCSEL 100, the laserlight 104 emerges from a surface 101 of the VCSEL 100. The light 104 isemitted at various angles that is often dependent on the current that isapplied to the VCSEL 100. Accordingly, some of the rays emitted by theVCSEL 100 have more power than other rays emitted by the VCSEL 100. Theangle 105 corresponds to the numerical aperture of the VCSEL 100. Thenumerical aperture can thus be used to identify the angles of the lightrays that have the most power. When the power of the light is carried inthe high angle rays, it is necessary to effectively couple the highangle rays to the receiver.

[0028]FIG. 2 further explains the relationship between the powercontained in the rays emitted by the VCSEL 100 and the angle at whichthe rays are emitted from the VCSEL 100. FIG. 2 illustrates the farfield effect of a VCSEL, and a graph 200 plots the degrees with whichrays leave the VCSEL against the relative intensity of those rays. Inthis example, the point 204 has lower intensity that the point 202. Therays that correspond to the point 204 are low angle rays while the raysthat correspond to the point 202 are high angle rays. In other words,the numerical aperture of the rays represented by the point 202 isgreater than the numerical aperture of the rays represented by the point204. Extending the graph to three dimensions, the far field plot of theVCSEL 100 thus has a doughnut shape and the power is concentrated in thelarger or higher angle rays emitted from the VCSEL 100. Efficientlycoupling a VCSEL or other light source that has a similar far fieldpattern requires that the higher angles be coupled to the fiber. Anoptical element such as a lens that is incorporated into a port shouldbe able to couple the high angle rays of the light source in order toachieve efficient coupling of the source to the receiver.

[0029]FIG. 3 illustrates an optical transceiver or port in accordancewith the present invention and more particularly illustrates a crosssectional view of an exemplary small form factor optical transceiver orport. The port 300 is molded from plastic or other suitable material andincorporates a lens 304, as indicated by the dashed box, as an integralpart of the molded port 300. The lens 304 of the port 100 includes alens surface 306 and the lens 304 has a thickness 305. The lens 304 isembedded inside of the lens access 310 of the port 300. The lens surface306 is the surface of the lens 304 that has optical power. The lenssurface 301 is typically flat and does not have optical power.

[0030] Because the optical power of the lens is concentrated in a singlelens surface, the design tolerances with which the lens should complyare reduced. If the lens 304 of the port 300 has optical power in boththe lens surface 304 and the lens surface 301, then it is necessary tomake each lens surface comply with design tolerances. In addition, it isnecessary, in this situation where each lens surface has optical power,to ensure that the mechanical position of the lenses is withintolerances in all translation and tilt axes with respect to each other.If the lens surfaces were to have positional errors, the performance ofthe lens 304 is reduced. By making the lens surface 301 substantiallyflat, these potential problems are reduced or eliminated. The flatsurface 301 therefore does not have cross positional tolerances, withrespect to the port or optical axis, because it has no optical power. Ifthe flat surface 301 does include errors along the optical axis, whichis typically normal to the flat surface 301, then compensation for thiserror can be made by slightly defocusing the source without incurringsignificant aberrations.

[0031] The port 300 is used to couple a source to a receiver. Forexample, the port 300 may be used to couple a light source such as aVCSEL with a receiver such as an optical fiber. Using this example, theport 300 can be connected or coupled with an optical fiber using thefiber access 308 which is formed by the fiber guide 312. The opticalfiber is inserted into the fiber access 308. A fiber stop 302 isincluded in the port 300 to ensure that the fiber is not inserted in theport 300 too far and to properly position the fiber with respect to theflat surface 301 of the lens 304. The fiber guide 312 thus surrounds aportion of the optical fiber. It is understood that the port 300 canhave other mechanical configurations that permit the port to beconnected with the light source and the receiver. In each case, the flatsurface 301 is properly positioned with respect to the optical fiber.

[0032] The lens surface 306 is typically located within the port access310, which is formed by source guide 312. The source guide 312 istypically configured to connect with a source such that the source isappropriately placed near the lens 304. The area between the focusinglens surface 306 and the flat lens surface 301 is typically filled withmolding material. The area 314 is also filled with molding material toenhance the mechanical stability of the lens without much absorption andscattering penalty.

[0033]FIG. 4 is a block diagram that illustrates an example of a lens400 that may be formed as an integral part of the port 300 illustratedin FIG. 3. The lens 400 includes a body 406. A flat lens surface 401without optical power is formed at one end of the body 406 of the lens400 while the focusing lens surface 403 of the lens 400 is curved andhas optical power. A source 402, which may be a VCSEL, is illustrated inFIG. 4 and the light emitted by the source 402 is being coupled to anoptical fiber 404 by the lens 400. It is understood that FIG. 4 isillustrative in nature and is not drawn to scale.

[0034] The light source 402 emits rays of light and the rays 408 arehigh angle rays and typically carry more power than the low angle rays410 as described in FIGS. 1 and 2. In order to efficiently couple thesource 402 to the fiber 404, the high angle rays must be properlydirected or focused on the fiber 404. The length 405 of the lens 400 isrelated to the magnification of the lens 400 and the lens surface 403 isan example of focusing means for focusing light from a source onto areceiver.

[0035] The fiber 404 has a numerical aperture that determines whichlight rays are accepted into and transmitted by the fiber 404. Rays thatare incident to the fiber 404 at too steep of an angle, which is greaterthat the numerical aperture of the fiber 404, are lost. In this example,the rays 408 are within the numerical aperture of the fiber 404 and areeffectively coupled. The lens 400, using the lens surface 403 and amagnification of 1.5 can couple, for example, a 0.3 numerical aperturesource to a 0.2 numerical aperture receiver.

[0036]FIG. 5 illustrates features of a lens that may be incorporatedinto a port. This illustration is intended as exemplary and the presentinvention is not limited to this example. The lens 500 has a diameter502 of 2 millimeters and a clear aperture of 1.6 millimeters. The lensthickness 506 is 3.41 millimeters +/−0.01 millimeter. The surfaceaccuracy of the focusing lens surface 510 has less than 0.3 micron sagerror over the clear aperture of the lens and less than 0.2 micron localsurface errors. The lens surface should not have visible scratches,digs, or bubbles under a 20×microscope. The centricity of the lens is+/−25 microns and the tilt is +/−1 degree.

[0037] These tolerances are exemplary in nature and help ensure that thelens is capable of effectively coupling a light source to a receiver. Asignificant advantage of this lens, as is Z illustrated in FIGS. 6A and6B below, is that reflections of the image back to the source arereduced or eliminated because the lens introduces aberrations withoutsacrificing the ability of the lens to effectively couple light. Thepresent invention is, therefore, not limited to these tolerances or tothis specific design, but extends to all lens or ports that reducereflections back to the light source.

[0038] For this example of the focusing lens surface, c=1.4265 andk=−1.292. The following table is a sag table that defines the lenssurface. All numbers are in millimeters. The y coordinate is 0 at thecenter of the lens. Y Coordinate SAG 0.000000e+000 0.000000e+0005.000000e−002 1.782537e−003 1.000000e−001 7.122236e−003 1.500000e−0011.599554e−002 2.000000e−001 2.836375e−002 2.500000e−001 4.417388e−0023.000000e−001 6.335972e−002 3.500000e−001 8.584321e−002 4.000000e−0011.115359e−001 4.500000e−001 1.403404e−001 5.000000e−001 1.721525e−0015.500000e−001 2.068620e−001 6.000000e−001 2.443550e−001 6.500000e−0012.845151e−001 7.000000e−001 3.272244e−001 7.500000e−001 3.723653e−0018.000000e−001 4.198212e−001

[0039]FIGS. 6A and 6B illustrate how the lens described above focuses asource on a fiber. FIG. 6A represents the light source and FIG. 6Billustrates the image of the source on the receiver or optical fiber. Inthis example, the points 601, 602, 603, 604, and 605 are selected at thesource 600. If the lens focuses these source points on the receiver,then the image would be points as well. The lens described herein,however, introduces aberrations or slightly defocuses the points601-605. The image is represented on the receiver 610 as images 611,612, 613, 614, and 615. The image 611 is from the point 601, the image612 is from the point 602, the image 613 is from the point 603, theimage 614 is from the point 604, and the image 615 is from the point605. The images 611, 612, 613, 614, and 615 are aberrated or slightlydefocused. However, the aberrated images are within and envelope 616that permits effective coupling with the optical fiber. The aberratedimages have good containment and are sufficiently far away from theedges of the fiber.

[0040] By introducing these aberrations into the lens, the lens or theport is still able to effectively couple the source to the receiver, butreflections from the image back to the source are reduced or eliminated.The spots or the images formed on the receiver are affected, forinstance, by the magnification of the lens and by the aberrationintroduced by the lens.

[0041] In other words, the images of the selected points are spots. Inthis example where the optical fiber has a diameter of approximately 60microns, the spots have a diameter of approximately 10 microns. The highangle rays are coupled by the port and reflection of the to image backto the source is reduced or eliminated by the aberrations introduced bythe lens of the port.

[0042]FIG. 7 illustrates a transform function of the lens describedherein. The line 700 illustrates the transfer function in terms ofspatial frequency in cycles per millimeter at a diffraction limit withno aberration. The lines 702, 704, and 706 illustrate the transferfunction with various aberrations. FIG. 7 illustrates how theinformation is translated with respect to frequency. The aberrationsintroduced by the lens reduces feedback while permitting the laser lightto be coupled.

[0043] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. In an optical communication system, an opticaltransceiver for coupling light from a source optical element to areceiving optical element, the optical transceiver comprising: a bodyincluding a source guide that connects the optical transceiver with thesource optical element and a fiber guide that connects the opticaltransceiver with the receiving optical element; and a lens formed as amolded part of the body, wherein the lens aberrates light from thesource optical element on the receiving optical element to reducefeedback, the lens comprising: a focusing lens surface that ispositioned within a source guide such that far field radiation emittedby the source optical element is directed to the receiving opticalelement; and a flat lens surface positioned within the fiber guide,wherein the flat lens surface does not have optical power.
 2. An opticaltransceiver as defined in claim 1, wherein the body further comprises afiber stop located within the fiber guide, wherein the fiber stoppositions the receiving optical element with respect to the flat lenssurface.
 3. An optical transceiver as defined in claim 1, wherein thelens further comprises a length that determines a magnification of thelens.
 4. An optical transceiver as defined in claim 1, wherein thefocusing lens surface comprises a clear aperture.
 5. An opticaltransceiver as defined in claim 1, wherein the focusing lens surfacecouples high angle rays from the source optical element on the receivingoptical element, wherein an image formed by the lens on the receivingoptical element is aberrated.
 6. In an optical communication systemwhere optical signals are coupled from one optical element to anotheroptical element, a port for coupling a source optical element with areceiving optical element, the port comprising: a port body including asource guide and a fiber guide, wherein the source guide is formed toconnect with the source optical element and wherein the fiber guide isformed to connect with the receiving optical element; and a lens formedas an integral part of the port body, wherein the lens receives lightgenerated by the source optical device and focuses the light on thereceiving optical device such that the light is aberrated to reducefeedback, wherein the lens comprises: a focusing lens surface, whereinthe focusing lens surface has a curvature that introduces aberrations inthe light being coupled with the receiving optical device such that animage on the receiving optical device is defocused; and a flat lenssurface.
 7. A port as defined in claim 6, wherein the focusing lenssurface has a clear aperture.
 8. A port as defined in claim 6, whereinthe lens has a length to magnify the light being coupled.
 9. A port asdefined in claim 6, wherein the focusing lens surface couples high anglerays from the source optical element on the receiving optical element,wherein an image formed by the lens on the receiving optical element isaberrated.
 10. A port as defined in claim 6, wherein a point lightsource from the source optical element is imaged as a spot on thereceiving optical element.
 11. A port as defined in claim 6, wherein theport further comprises a fiber stop formed within the fiber guide,wherein the fiber stop positions the receiving optical element near theflat lens surface.
 12. A lens disposed with a molded port for coupling asource optical element with a receiving optical element, the lenscomprising: focusing means for aberrating light from the source opticalelement such that an image of the source optical element formed on thereceiving optical element is defocused to reduce reflections back intothe source optical element; a flat lens surface that does not haveoptical power, wherein the flat lens surface is positioned near thereceiving optical element such that a tilt of the flat lens surface doesnot affect the coupling of light between the source optical element andthe receiving optical element; and a length that determines amagnification of the lens and a position of the source optical elementwith respect to the receiving optical element.
 13. A lens as defined inclaim 12, wherein the focusing means further comprises a focusing lenssurface.
 14. A lens as defined in claim 13, wherein the lens furthercomprises a clear aperture defined by a sag table.
 15. A lens as definedin claim 13, wherein the tolerance of the sag table is less than 0.1microns.
 16. A lens as defined in claim 13, wherein a point from thesource optical element is imaged as a spot on the receiving opticalelement, wherein the spot has a diameter on the order of 10 microns.